Gas-purification process and apparatus



www l 'GAS PURIFICAT'ION PROCESSAND ArxARATUs Filed Nov. z4 19m Patented t". 2e, reza l S TNT IEI'U'G'IENI?. H. BIRD, vOF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO THE KOPPERS COMPANY, OF PITTSBURGH, :PENNSYLVAN'IILA, A CORPORATION OF PENNSYLVANIA;

GAS-PURIFECATON PROCESS AND APPARATUS.

Application led November 24., 1922. Serial No. 603,062.

This invention relates to the removal of hydrogen sulphide and other noxiousconstituents, such as hydrocyanic acid, from gases containing them.- An object of the in- .vention is to provide an improved process for treating such gases, whereby not only the ent agent, such asa solution of sodium carbonate, to absorb the noxious constituents from the gas, and then subjecting the absorbent agentfcontaining the absorbed impurities to aeration to remove the absorbed impurities and to regenerate lthe absorbent agent so as to render it available for further gas purification. The present invention, however, is not confined tothe process just referred to, but is broadly applicablehto a varietynof processes based on the employment of Aliquid media for gas purification.

A process such as that'of the above mentioned prior patent may be practiced in two essential parts of apparatus, i. e., the cham-` ber in which the gas is brought into contact with the purifying liquid, and the chamber in which the liquid containing the absorbed impurities is regenerated. In practice the first chamber is designated as the absorber and the second the actifier. terms will be employed in the following description.

The removal of tlieflast traces 'of the hydrogen sulphide from the gas is`a requirement that most-gas companies'must meet,

being imposed by law in most places. 'By this invention, vthere is provided a process and apparatus whereby the last traces of hydrogen sulphide' are removed from the.

gas by a system of liquid purification, complete in itself, without any resort whatever to ordinary iron oxide purification of the gas discharged from the liquid purification These two plant. Hydrocyanic acid is also completely removed, with resulting improvement in the quality of the gas. y

In addition to the generalobject recited above, the invention has for further objects such other. improvements or advantages in operation and results as lare found to obtain in the processes and apparatus hereinafter A described or claimed.

In the accompanying drawings forming a .part of this specification and showin for purposes of exempliiication, a pre erred form and manner in which the invention may be'embodied and practiced, but without limiting the claimed invention specifically to i said illustrative instances:

j Figure 1 is a sectional elevation of one form of apparatus for carrying out the improved process of the invention;

Fig. 2 is a plan view of the apparatus illustrated in Fig.4 l;

.F ig. 3 is a ldiagrammatic view showing mechanism controlling intermittent pump.

ing of regenerated solution back to the secondor final absorber.

In its present embodiment, the invention is applied to the purification of cokel oven gas, and, for convenience, the present description will be confined to this use of the invention.

Features of the invention are, however, ap-

plicable to other useful applications, for example, to other gases; Consequently, the in- Ivention is notconfined in scope to the specific use and embodiment herein described as an illustrative example.

For effecting the absorption of the sulphur compounds and other impurities from the gas, there is employed'a water solution of an alkaline compound having an aflinity for hydrogen sulphide. A number of the compoundsfof the alkali metals and alkaline earths possess-this property. -A solution of sodium carbonate in water is especially suitable for effecting the absorption of sul hur from the gas, because of the great a ity which .a water solution of sodium carbonate has for hydrogen sulphide and because of the cheapness and availability of this sodium salt. A solution of .sodium carbonate is strongly basic in its properties.y When sodium carbonate dissolved in water is brought into contact with gas,.such ascoke oven gas, containing carbon dioxide and hydrogen sulphide. carbon dioxide-is absorbed'. and sodium bicarbonate is formed, as may for example, be illustrated' by the following explanation The solution of sodium carbonate will also effect the absorption from the'- gas of such sulphur `compounds as hydrogen sulphide, HZS. The absorption of hydrogen sulphide may be. illustrated by the following equation:

Na2oo3+H2s=Nanoos+Nans In applying the above to the absorption of sulphur froma gas, it is preferable to u se a dilute solution of .sodium carbonate 1n water. vA concentration from about two to tions v Andalsm.

NaHoo3+Nans=Na2oos+n2s 'Ihe rapid and thorough aeration greatly promotes the foregoing reactions by rapidly removing the gaseous products,-as` well as checking the formation of thiosulphates, and

the solution gives up its hydrogen'sulphide land is rejuvenated. Instead of air, another similarly inert gas may be used in the actier.

In carryingxout the invention, the gasto i be purified is firstA passed thirough the primary absorberA. Here it is'bro'ught into Contact lwith a solution of sodium carbonate, pumped from the primary sump B through pipe l, pump C, pipe 2 and sprays 3. The impure gas enters the bottom of the primary absorber through the pipe 50, and the gas'- fromwhich the bull,of'the impurities have been removed discharges from the top of the primary absorber vthrough the pipe' 51. The solution containingthe absorbed impurities from the bottom of the primary absorber runs through pipe 4 and is discharged "by sprays 5 into the top of the primary actiier Here the absorbed impurities are removed by means of air blown into the bottom of the actifier, through the inlet 52. The air escapes through the stack E which is shown in this case as passing from .the top4 of the primary actifier up through the middieof the prrmary absorber. The solution thus regenerated runs intov primary sump B and is used over and'over again.

An important feature of the invention is that the major portion of the'impurities are removed from the gas in the primary absorber, and the remaining lesser portion re' moved by a second operation employing a move all of the hydrogen'sulphide. The

correspondingly smaller bulk of liquid which has undergone a second revivification,4

It has been found to be most convenient and economical to operate in such a way that approximately 90% of the hydrogen 'sulphide and hydrocyanic acid are removed from the gas in the primary system. Absolute purification is difficult of accomplishment in a single stage system of this sort without very greatlydecreasing itsv capacity. `When a single stage liquid purification system is employed, a little hydrogen sulphide remains in the form ofalkaline hydro-sulphide in the solution going from the actifier D to the primaryy sump B. In order to use this solution to remove the last traces of hydrogen sulphide from the gas, in the seoond stage of the process, the last traces of hydrosulphides must be removed from the solution. On the other hand, since only traces of hydrogen sulphide remain in the gas'pa'ssing out of the primary absorber A,

only ya small volumeof solution will be required to furnish the alkali necessary to reessential l'condition is'that the vsolution thus employed for the removals-.of these traces from the gas be free fromv sulphide compounds such as exerta partialpressure with respect to hydrogen sulphide, and, .as a further important condition, that the solution, in the'second stage, be distributed over a very large s'urfaceto insure thorough contact with the gas. Analogou's considerations apply to hydrocyanic acidand cyanide eom- 1"" pounds. f'

In order, then, to removeA even the last tracesof hydrogen sulphide from the gas, a portion of the actifiedv solution is withdrawn from the primary' system through pipe 6 105 'and is introducedby sprays 7 into a seeondary actifier F. n' usual practice, the solution thus 'withdrawn may be about one tenth of the'volume of solution in circulation through the primary system. blown into the bottom of the secondary `actifierFthrough the inlet 53 and removes the last traces of sulphide and hydrocyanic acid compounds, from the solution. The air from the. secondary actifier escapes through 115 the outlet Gr. The thoroughly cleaned Solution flows from the bottom of the secondary actifierinto the'secondary sump H. The operation of the secondary actilier may be carried on continuously, but it has been 1120.

Air 'is 110 I distribution of the solutionover the material I rial offering relatively large surfaces j an'd capable of holding a considerable amount of liquid by adhesion. In practice there has been useda iinal absorber lilled with shavings, capable of holding suicient solution to remove the last traces of hydrogen .sulphide from thegas for a period of three v hours. The active surfaces of the secondary absorber are of Vsubstantially greater area than those ofthe primary absorber.

The gas passes from the primary absoroer` A through pipe J into the bottom of the final absorber I. When the second sump'H is full a float W on this sump automaticallystarts the secondary pump Kwvhich pumps the clean solution through pipes 8 and -9 and sprays. 10, drenching the material in the final absorber and Washing out any fouled solution. This fouledsolution runs through pipe 1l into primary sump B. The actual time of pumping may -be varied considerably, but in practice, it ordinarily takes from 10 to 20minutesto empty the secondary sump. The pump' K then automatically stops and may Anot be started again until the sump H is refilled.A

A form of apparatus controlling the intermittent pumping of the solution from the sump H to the iinal absorber I' is shown diagrammatically in Fig.3; The float W in the sump H is suspended from-a lflexible rope or cord which runs over supporting pulleys 6l. When the liquid in said sump rises to a predetermined highY level, the operatinglugv 62 on the rope 60 movesthe pivot'd switch arm 63 to cause themovable contact member 64 toengage the iixed contact member 65 and closevthe motor circuit 66 of the motor 67 which operates the' pump `K. But, when the liquid in the said sump falls to a predetermined low 1evel, the lowering of the float W will cause the lug 68 to rise and move the arm 63 to break the motor circuit. Until such predetermined low level is attained, however,'thecontact will remain in circuit closing' position.

Besides the great advantage obtained-by completely eliminating oxide purification, it.

' has' been found" possible by this invention to reduce l greatly the size of the "apparatus necessary fork removing the last traces of hydrogen sulphide. A. reduction of 50%.` or more has Ybeen effected in'fthis'r'spect. Any' soda. which it is necessary to add to the system to replenish losses, is preferably added to the solution in the secondary sump so that the fresh soda- Will alvva s be used first to remove the 'last traces o hydrogen sulphide frorrrthe gas.

The invention as hereinabove set, forth 1. The process of purifying gases which consists in? passing the gas. into' Contact With a relatively large volume of. alkaline absorbent agent to absorb the bulk ofthe hydrogen sulphide impurities from the gas, then passing thethus purified gas into cont-act with a relatively smaller volume of alkaline absorbent agent to absorb the residue of hydrogen sulphide from the gas; subjecting the absorbent agent discharged from "the iii-st absorption stage .to aeration to rel. move the absorbed impurities commingling the( absorbent agent' discharged from the second absorption stage with the aerated so-A lution from the first absorptionv stage; with,

drawing part of the solution from the thus ,commingled bulk and subjecting such Withdrawn part to individual aeration; .interq mittently recirculating the solution from the last mentioned aerationstage back to the second absorption stage; and continuously recirculating vthe remainder'of the solution from the rst mentioned aeration stage back to the primary absorption stage; substantially as specied. i

2. The process of purifying gases which consists in: passing the gas into eontact'with a relatively large volume of sodium carbonate solution to absorb the bulk of the hydro gen sulphide impurities from the gas, then passing the thus puriiied gas into contact `With a relatively smaller volume of sodium 'carbonate'solution to absorb the residue of .hydrogen sulphide from-the gas; subjecting thesolution discharged `from the first absorptionstag'e to'aeration to remove the absorbed impurities, commingling lthe solution discharged from the second absorption stage with the aerated solution from the first absorption stage;` withdrawingpart of the solution from vthe thus commingled bulk and subjecting such Withdrawn part to individual aeration; intermittently recirculating the solution from `the .last men- 'tioned aeration'stage'- back' to the second absorption stage; and continuously recirculatin the remainder of the solution from the4 rst mentioned aeration stage back to the primary absorption stage; substan-V tially. as specified.-4

a 3. The processor purifying gases which Y rconsists in :"passingthe gas into. contact with a relatively large volume .of alkaline liquid absorbent agent to 'absorb the bulk of thehydrogensulphide impurities from the gais", then passing the thus purified vas into contact with a relatively smaller vol urne of alka line liquid absorbent agent distributed over a relatively large area to absorb the residue of hydrogen sulphide from the gas;` sub vWith a relatively smaller volume of sodium carbonate absorbent solution distributed over i a relatively large area to absorb the residue of hydrogen sulphide from the gas; substantially as specified.

5. The process of purifying gases, which consists in: passing the gas throughfnonreacting solid material drenched with a soy lutionv reactive tothe impurities in the gas,

ldischarging the solution from the non-react ing material, 4regenerating it, and intermittently drenching the non-reacting material with the regenerated solution; substantially as specified.

6. The process of'purifying gases, which consists in: passing the gas through non-reacting solid material drenched with a solution i'eactive to the impurities in the gas, disphideconstituents from gases, which consists' charging the solution from the non-reacting material, aerating it, and intermittently drenching the non-reacting material with the vaerated solution; substantially as specified.

7 The' process of removing hydrogen sulin: passing the-gas through `non-reacting solid material drenched with a solution resolution; substantially as specified.

. 8. The process ot puritying gases, consists in: passing the gas through a massy active to the hydrogen sulphide impurities in the gas, discharging the solution, regenerating it, and intermittently drenching the non-reacting material lwith the regenerated which of' non-reacting solidinert material drenched with and holding for a 'considerable period of time al solution reactive to the impurities in the gas, discharging the solution from the. non-reacting material, regenerating it,

and Ad reiiching the non-reactinrrmaterial with the vregenerated* solution; siibstantially as specified.

9. The process of removing hydrogen sulphide constituents from gases, which consists ingvpassing the gas through a mass of'nonreacting solid inert material drenched withand holding for a considerable-period of time 'a Ysolution reactive to the hydrogen sulphide impurities in the ga's,idischarging consists in: subjecting the" gas to a primaryv the solution, regenerating it, and drenching the non-reacting material with the regenerated solution; substantially as specified.

- ll0. The process of purifying gases, which absorption stage iii-which the gas is'brought Ainte contact with a solution reactive to the reacting solid material' drenched with a Lceojrai gas, and then passing' the gas through nonreacting solid material drenched with a so? lution reactive to such impurities to remove the residue. of the impurities from the gas; substantially as specified.

l1. The process of purifying gases, which consists in: passing the 'gas through nonsodium carbonate solution to remove the vhydrogen sulphide impurities from the gas;

substantially as specified.

12. ln a process for the purification of gas by circiilatinga liquid absorbent agent continuously through a gas purification stage and a regeneration stage, the combination of steps which consists in': withdrawing a portion of the liquid from the regeneration stage, subjecting it to .further regenerationand bringing-it into contact with the gas from tlielgas puriiicationstage to remove the last traces of impurities;.sub

stantially as specified.

A13. lin a process for the purification of .gas by circulating a liquid absorbent agent continuously through a Agas purification stage and a regeneration stage, the combination ofsteps Which consists in: withdrawing a portion of the liquid. from the Aregeneration stage, subjecting it to further regeneration, and pumping the furthei lregenerated portion intermittently over non-reacting solid material in contact with the gas' continuouslyvpassing from the purification stage; substantially as's'pecified.

14.7ln a process for the purification of gas by .circulating aliquid absorbent agent continuously through a gas purification 'stage and an aeration stage, the combination of steps'which consists in: withdrawing a portion of the liquid `from the aeration stage, subjecting it to further aeratioi'and bringing it into contact with the gas from the gas purificationstage to remove the last races of impurities; substantially as kspeci- 15'. ln a vprocessYf'or the'purification of gas by` circulating a liquid absorbent agent continuously through a gas` purification stageand an aeration stage, the combination ofsteps which consists in: withdrawing a portion of the liquid from thefaeration stage, subjecting it to furtheraeration, and pumping the further aerated portion intermittently over non-reacting solid material in contact with the gas continuously passing from the purification stage;- substantiallyas specified. l

16. ln a process for the purification `of gas by circulating a sodium carbonate solution continuously througha gas purification stage and a regeneration stage, the combination of steps which consists in: withdrawing a portion oit-the liquid from the regenerathe absorbed impurities and subjecting it to tion stage, subjecting itto further regeneration and bringing it into contact with the gas from the gas purification stage 'to re move the last traces of impurities; substantially as specified.

17. The process `for the purification of gas consisting in continuously passing the gas in a primary purication stage through an alkaline absorbent agent, continuously discharging .the absorbent agent containing aeration toremove ,the -absorbed impurities,- continuoufsly circulating the regenerated absorbent vagent back tothe primary purificationl stage, withdrawing a portion of 'the liquid :tromv the aeration stage, treating it to remove the last tra/ces of impurities, andA bringing it -into contact with the gas from the primary purification stage; substantiallyl as speciied. y 18. Apparatus for purifying gases, /embodying: a primary absorber, a primary actifier, a secondary absorber and asecon'd-fv ary actifier, means' for withdrawing solution from the' primary actierand passing it over the secondary actier, and means for pumping the solution from the secondary actiiier 'over the secondary stantially as specified.

19. Apparatus for' purifying gases, em-

bodying: a primary absorber, -a primary.l

actifier, a secondary absorber, and a secondary actiiier having a bed of non-reacting solid material, means for withdrawing solu'- tion from the primary actier and passing it over the seconda actifier', and means for pumping the solutlon from the secondary absorber; subactifer over the secondary absorber; substantially asspecitied.

20. Gaspurification apparatus, embodying: an absorber filled with non-reacting s olid material, a sump,.an aerating tower connected with saidsump, means for pump ing olution from the absorber over the aerating tower, and means intermittentlyl pumping the aerated solution from the sump and distributingit over the material in the solution in the sump, for intermittently` pumping the aerated solution from the sump and distributing it over the material in the absorber; substantially asspecied.

involves passing the gas in Contact with` a liquid absorbent agent in a gas purication stage, discharging spent liquid from the gas .purification stage, revivifying spent liquid 'discharged from'the gas purification stage,

and recirculating reviviied liquid to a gas puriication stage, the improvement which comprises intensively actifying a portion only of thespent liquid that is dischargedA from the gas purification stage.

In testimony. whereof I have hereunto set my hand.

UGENE' H. BIRD.

22. In a .process of purifying gases thatmiv 

